ESPE Abstracts

Background: Bone mass is low in obese children when measured by conventional techniques. However, these imaging modalities cannot quantify alterations in bone microstructure and strength. High resolution peripheral quantitative computed tomography (HRpQCT – isotropic voxel size 82 mm) provides the resolution required to determine 3-dimensional in-vivo bone microstructure; microfinite element (microFE) analysis of HRpQCT images provides insight into skeletal biomechanical properties.

Method: Children aged 8–15 years matched by gender and pubertal stage were recruited into lean and obese groups (18 pairs). Bone micro-structural parameters were quantified using HRpQCT. MicroFE was used to determine bone stiffness, estimated failure load, load carried by the trabecular and cortical bone, and the average Von Mises stresses. Bone strength index was calculated using (BSI (mg²/mm⁴)= Density_total²×Area_total). Lean and fat mass were measured by DXA.

Results: Lean and obese children were 12.9±2.0 and 12.6±1.9 years (P=0.23) respectively. There was no difference in height SDS between the groups (1.12±1.34 vs 0.96±1.41, P=0.67). Radial cortical porosity (mean difference −0.01 (95% CI:−0.02, −0.004), P=0.003) and cortical pore diameter (mean difference −0.005 mm (95% CI: −0.009, −0.001), P=0.01) were lower in obese children. Tibial trabecular thickness was lower (mean difference −0.009 mm (95% CI:−0.014, −0.004), P=0.003) and trabecular number was higher (mean difference 0.23/mm (95% CI:0.08, 0.38), P=0.004) in obese children. There was no difference in radial and tibial bone strength proxies. Subtotal fat mass % positively correlated with radial cortical thickness (r=0.43, P=0.008) and density (r=0.36, P=0.02) whereas lean mass correlated with radial cortical (r=0.44, P=0.007) and trabecular (r=0.55, P=0.007) area. Subtotal fat mass % negatively correlated with tibial trabecular density (r=−0.37, P=0.03) and thickness (r=−0.62, P<0.001).

Conclusion: Obesity in children has a positive effect on cortical microstructure at the distal radius and a negative impact on trabecular microstructure at the distal tibia. However, these changes were not sufficient to impact on bone strength.